1. Field of the Invention
The present invention relates generally to a self-calibrating apparatus and method in a mobile transceiver, and in particular, to an apparatus and method for self-calibrating non-linearity and mismatching between orthogonal signals generated in a mobile transceiver.
2. Description of the Related Art
Generally, non-ideal characteristics such as non-linearity, mismatching, etc., are the fundamental causes of performance degradation in a mobile transceiver. Non-linearity is caused by a power amplifier and a mixer in a mobile transmitter, and is caused by a low-nose amplifier, a mixer, and an active filter in a mobile receiver. The non-linearity occurring in the mobile transmitter increases interference between neighbor channels. Therefore, non-linearity raises desensitization, blocking, cross-modulation, and inter-modulation problems in the mobile transceiver.
Mismatching is caused from gain and phase inconsistencies between an in-phase channel signal (or I-channel signal) path and a quadrature-phase channel signal (or Q-channel signal) path in a mobile transceiver that transmits an I-channel signal and a Q-channel signal by a constant phase difference. Mismatching occurring for such a reason increases a bit error rate (BER), leading to a decrease in performance of the mobile transceiver.
Therefore, in order to improve performance of a mobile transceiver, a method for calibrating (or compensating for) the non-linearity and mismatching must be provided.
FIG. 1 is a diagram illustrating a system for calibrating non-linearity and mismatching occurring in a conventional mobile transceiver. Referring to FIG. 1, a signal generator 110 generates an electric signal, or a test signal, set by a measurer (or user). The test signal is provided to a mobile transceiver 120 to be tested. The mobile transceiver 120 outputs the test signal as measured data through a given processing procedure. The measured data is provided to a measuring equipment 130. The measuring equipment 130 outputs a response characteristic for the test signal based on the measured data so that the measurer can be aware of the response characteristic. Equipment such as a frequency analyzer and an oscilloscope can be used as the measuring equipment 130. The measurer determines whether to calibrate non-ideal characteristics such as non-linearity and mismatching in the mobile transceiver 120, by analyzing the response characteristic for the test signal. If the measurer determines to calibrate the non-ideal characteristics, the measurer manipulates a control equipment 140 to provide a control signal for calibrating the non-ideal characteristic to the mobile transceiver 120. The mobile transceiver 120 calibrates the non-ideal characteristic by calibrating corresponding parameters according to the control signal.
In alternative implementation, the calibration can be achieved based on the measured data output from the mobile transceiver 120 without manipulation of the control equipment 140 by the measurer. The control equipment 140 must generate a control signal for calibrating the non-ideal characteristic in response to the measured data. The control equipment 140 commonly uses two kinds of calibration methods: an analog trimming-type calibration method and a digital trimming-type calibration method. However, the analog trimming-type calibration method is expensive and is not adaptive to variation in an environment such as a temperature. Additionally, in the digital trimming-type calibration method, a circuit for measuring a non-ideal characteristic and an operation circuit for calibrating the measured non-ideal characteristic must be further added, and considerable power consumption occurs for this complicated operations.
Another example of calibrating mismatching in a mobile transceiver is disclosed in U.S. Pat. No. 6,009,317 assigned to Ericsson, the contents of which are incorporated herein by reference. However, the method proposed in this reference can only compensate for mismatching in a receiver by a digital processor. In addition, for the compensation, an external signal generator is used. That is, the method proposed in the reference cannot calibrate all non-ideal characteristics that are commonly generated in a mobile transceiver, and cannot solve the existing hardware complexity problem.